A majority of the loudspeakers manufactured and used today follow a relatively old basic design. A common design of a loudspeaker comprises a permanent magnet, a movable coil within a magnetic field produced by the permanent magnet, and a membrane attached to the movable coil. An alternating electric current flowing through the coil causes the coil to oscillate within the magnetic field, thus driving the membrane, which in turn produces a sound. This basic design is used for a large number of electrodynamic loudspeakers, which typically have a relatively large back volume behind the membrane, i.e., at a side of the membrane opposite to the side of the membrane from which the sound waves are propagated to the environment. The size of the back volume of an electrodynamic loudspeaker is typically reciprocally related to the intended frequency range of the loudspeaker, that is, a loudspeaker of a low frequency range typically has a relatively large back volume.
The ongoing desire to miniaturize electronic components and electromechanical components has caused extensive research in the field of micro-electromechanical systems (MEMS), which are small mechanical devices driven by electricity. MEMS became practical once they could be fabricated using modified semiconductor device fabrication technologies, normally used to make electronics. These fabrication technologies include molding and plating, wet etching (KOH (potassium hydroxide), TMAH (Tetramethylammonium Hydroxide)) and dry etching (RIE (Reactive-Ion Etching) and DRIE (Deep Reactive-Ion Etching)), electro discharge machining (EDM), and other technologies capable of manufacturing small devices. Loudspeakers are a possible application of micro-electromechanical systems. In order to achieve a sufficient sound pressure level (SPL), loudspeakers fabricated by means of MEMS technology typically need to be arranged as an array comprising a plurality of basic loudspeaker elements.